When I try to use Qt Creator 4.3.1 (Qt 5.9.1) and I select New Project > Qt Quick Application, on the right side the only supported platforms is Desktop. I added the path to JDK, SDK, and NDK in Qt Creator. I have a warning in Tools > Options > Devices > Android.

So I installed Qt Creator 4.0.3( Qt 5.6.1) and when I select New Project > Qt Quick Application, on the right side the supported platforms are Android Device and Desktop. I added the path to JDK, SDK, and NDK in Qt Creator. I have a warning in Tools > Options > Devices > Android.

@WhatIf I've found a workaround for that: see this post. There is also another, more hacky solution: modify your *.pro.user file and replace every occurrence (there will be 3) of
"android--1" with an existing API from your SDK, for example: "android--23" - however, Qt Creator often reloads and saves the .user file, so this solution is very unstable.